For example, there has been developed a technology of displaying a portion traced by a presenter or the like on a display surface of a display apparatus, such as a liquid crystal display and a plasma display, in a special aspect which can distinguish the portion from another video image on the display surface. For example, as shown in a patent document 1, there has been developed a technology in which an infrared sensor or the like is embedded in advance in the display surface and the presenter traces the display surface with a special pen, which irradiates infrared light, to thereby display a portion pointed by the presenter or the like with a predetermined marker on the display surface on the basis of the detection result of the infrared light by the infrared sensor. Alternatively, the same construction can be employed by using e.g. ultrasound or the like, instead of the infrared light. Moreover, for example, there has been also developed a technology in which a touch panel is displaced in the front of the display surface and a portion touched by the presenter is correspondingly displayed with a predetermined marker on the display surface.
Patent document 1: Japanese Patent Application Laid Open NO. Hei 3-316770